A parabola has x-axis values of -3 and 5. And it symmetry axis is: x = 1

The a value is negative, but i cannot say what its exact value is.

It says to prove that

Here's what i did:

And now i KNOW that must be equal to but i have no idea how to prove it

Please help guys.

EDIT: Sorry, i forgot to mention that there is also a graph

I presume that "x-axis values of -3 and 5" means these are the x intercepts (-3, 0) and (5, 0)?

Then
is as good as you are going to get with the current information. The only thing you can do with it now is to find the axis of symmetry, which is supposed to be the line x = 1. But:
has an axis of symmtry at
and the "a" cancels out naturally. So we have no new information here.

I presume that "x-axis values of -3 and 5" means these are the x intercepts (-3, 0) and (5, 0)?

Then
is as good as you are going to get with the current information. The only thing you can do with it now is to find the axis of symmetry, which is supposed to be the line x = 1. But:
has an axis of symmtry at
and the "a" cancels out naturally. So we have no new information here.

I couldn't read it that well, but it appeared to give a = -1 explicitly and I can construct the parabola for a = -1/2, a = -1/sqrt(3), etc. with intercepts at x = -3 and 5 with an axis of symmetry x = 1 (as well as for a = -1.)

I couldn't read it that well, but it appeared to give a = -1 explicitly and I can construct the parabola for a = -1/2, a = -1/sqrt(3), etc. with intercepts at x = -3 and 5 with an axis of symmetry x = 1 (as well as for a = -1.)